The present invention relates to improvements in a method and apparatus for ascertaining the quality of ball striking implements, such as tennis rackets, squash rackets and the like. For the sake of simplicity, the following discussion of the state of art will refer to tennis rackets with the understanding, however, that the method and apparatus of the present invention can be used with equal advantage for ascertaining (i.e., testing) the quality of a wide variety of other types of ball striking implements and/or parts thereof.
At the present time, the quality of tennis rackets is ascertained by subjecting them to a static test. As a rule, the racket is placed on a suitable support so that it is at a standstill, and a selected part of or the entire racket is thereupon subjected to the action of a force which tends to move the racket or a selected part thereof out of a position of rest. The racket (or a selected part thereof) thereby undergoes an elastic (or even plastic) deformation. For example, the application of the force can entail a bending or flexing of the frame and/or a bending or flexing of the strings which constitute the netting of the racket. The ratio P/x of the magnitude of the applied force (P) and the extent of the resulting deflection or deformation (x) of the frame and/or netting is presently considered to constitute a parameter which is indicative of the tension of the netting. This parameter (also called the spring constant) is more accurately indicative of the behavior or action (i.e., quality) of the racket in actual use than another presently contemplated parameter, namely the elasticity of the strings (measured in kp) because such elasticity can be ascertained only during stringing of the netting.
The aforediscussed conventional methods of ascertaining the quality of tennis rackets exhibit a number of serious drawbacks. Thus, the apparatus which can accurately ascertain the value of P/x are rather complex, expensive, prone to malfunction and bulky so that they cannot be readily transported to the location of actual use of the racket. The monitoring of the elasticity of strings in kp and the ascertained value are not a reliable indicator of the quality of a tennis racket because they do not take into consideration the dimensions of the frame and, consequently, such information does not enable the user of the racket to estimate or ascertain the likely behavior of the implement in actual use. Still further, all heretofore known static tests of the quality of tennis rackets exhibit the drawback that the results of measurements are distorted due to friction in the regions where the strings intersect each other. The resulting damping action constitutes a drawback which is characteristic of each static testing procedure. In addition, a static quality measuring procedure does not furnish any indications regarding an essential aspect of the quality of a tennis racket and/or its netting, namely its dynamic behavior during play. Such dynamic behavior exerts a deciding influence upon the length of intervals of contact between the netting and the ball.